Using DFS, target will be target - root->val, remember to pop_back current vector;

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * @param root the root of binary tree
     * @param target an integer
     * @return all valid paths
     */
    vector<vector<int>> binaryTreePathSum(TreeNode *root, int target) {
        // Write your code here
        vector<vector<int>> results;
        vector<int> cur;
        dfsHelper(root, target, cur, results);
        return results;
    }
    void dfsHelper(TreeNode* root, int target, vector<int>& cur, vector<vector<int>>& results) {
        if (root == NULL) {
            return;
        }
        cur.push_back(root->val);
        if (root->left == NULL && root->right == NULL && root->val == target) {
            results.push_back(cur);
        } 
        else {
            target = target - root->val;
        } 
        dfsHelper(root->left, target, cur, results);
        dfsHelper(root->right, target, cur, results);
        cur.pop_back();

    }
};